Sentry provides full-stack visibility to help developers identify the root cause of slow applications by monitoring performance and errors across multiple projects and services. It captures distributed traces consisting of transactions and spans, allowing teams to see how slow operations in one project impact other projects, and identifies third-party dependencies. With Sentry's SDK, developers can monitor changes in their code and measure metrics like throughput, Apdex, User Misery, and transaction duration to display the impact of errors across multiple systems. This enables teams to quickly find performance issues' root causes and solve them, rather than trying to fix incorrect spans, ultimately saving time and improving application stability.